She went on a buying spree, picking up at least 17 companies, most notably the social blogging site Tumblr for $1.1 billion. Long languishing products were revamped, including the site’s home page, Flickr and Yahoo Mail. And Mayer achieved important but largely intangible goals, like restoring a sense of momentum at the company and improving employee morale – despite the loud criticism of her early decision to ban telecommuting.

Observers mostly applaud what she’s accomplished.

“It was a ship dead in the water until she came along,” said Greg Sterling, senior analyst at Opus Research in San Francisco. “She’s given it credibility on the consumer side that it didn’t have.”